Fish deaths caused by faulty pump

Three of about 20 brown trout found dead in Mill Creek, near Arrowtown, earlier this month. Photo / Otago Regional Council.

About 20 brown trout found dead in Mill Creek, near Arrowtown, were electrocuted because of a faulty submersible pump, the Otago Regional Council says.

Earlier this month, ORC chief executive Peter Bodeker said the council was investigating the cause of the fish deaths after being first notified by Fish and Game on June 2.
More were found during a site visit on June 7.

The council's environmental officers collected water samples at several points along the creek, near Speargrass Flat, on two occasions, both up and downstream of where the dead fish were found.

Those samples were analysed by two laboratories to determine  the level of pesticides,  other chemicals and heavy metals, as well as the overall quality of the water in the creek and a neighbouring wetland.

The analysis found no high levels of chemicals or heavy metals, except aluminium in the vicinity of the pump.

Meanwhile, two of the fish were sent to the Cawthron Institute in Nelson for autopsy, which showed no sign of poisoning or disease.

Yesterday, ORC environmental monitoring and operations director Scott MacLean said the investigation "strongly points" to the faulty pump electrifying the water and killing the fish.

ORC environmental officer Richard Heywood noticed the submersible pump in a privately owned wetland adjoining the stream while he and colleagues were collecting the water samples.

Mr Heyward recalled Fish and Game staff commenting it was as if "something" was creating a magnetic field which was attracting the fish, and realised  most of the dead fish had been reported as being near the pump's intake.

After he talked to the neighbouring landowner, an electrician checked the pump and found  it had a faulty float switch, sending current directly into the water and electrocuting the fish.

Because the pump wasn't operating all the time, the fish were being affected sporadically.
Mr MacLean praised the landowner for getting the pump checked and then arranging to have it removed as soon as the fault was identified.

"It's a great example of people working together," Mr MacLean said.

"It's a relief to be able to confirm that water pollution was not a factor in these deaths and that there is a simple explanation and an easy solution in this case."